Guidewires have long been used to facilitate diagnostic and therapeutic medical procedures. Generally speaking, a guidewire is the initial member inserted into a body cavity during many transluminal procedures. A guidewire is an elongated fine wire device intended to readily pass through body passageways to a location at which a medical procedure or treatment is to take place. Thereafter, in a typical arrangement, a catheter is threaded over the thus inserted guidewire, with the catheter following the pathway defined by the guidewire. In general terms, a guidewire is flexible, at least at its remote distal end tip.
Remote distal end tip flexibility is often enhanced by providing one or more fine coils at the distal portion of the guidewire and securing these coils to the distal end of the guidewire's core. Typically, this securement application also includes a rounded distal tip that imparts some atraumatic characteristics to the guidewire. In the usual approach, these components are secured together by soldering, brazing, welding or by using an adhesive such as ultraviolet-curing adhesives, catalytic-curing such as epoxy or anaerobic adhesives such as cyanoacrylate adhesives.
Distally tapered guidewires are generally composed of a stainless steel or austenitic metallic core which is not amendable to heat treatment for hardening the base metal. Stainless steel alloys employed in the medical field generally have a high chromium and low carbon content to provide resistance to oxidation and corrosion. Stainless steel or austenitic alloy guidewires are amendable to work hardening but the final process yields a wire that is hardened primarily in the outer layers. Any hardness developed by the work process decreases or is totally absent as the center of the core is approached where it remains relatively soft. After stainless steel or austenitic alloy guidewire cores are work hardened, they are distally tapered by standard diameter reduction processes, which exposes the relatively soft inner cross sectional layers and becomes the entire core of the distal end. This results in the stainless steel guidewire having inherently disportionate hardening throughout the length of the wire yielding suboptimal torsional characteristics. Inconsistent proximal to distal rotational movement makes it difficult for the clinician to penetrate small blood vessels while inadequate hardness affects the guidewire's catheter tracking capabilities. Stainless steel guidewires that suffer from inadequate entire cross sectional area hardening do not have high torsional capabilities for allowing the navigation through tortuous coronary, kidney or neurological vessels. In addition, such guidewires can suffer from snap or have unpredictable final tip positioning. Furthermore, it is important for a guidewire to be able to conform over sever curves and sharp angles without causing plastic deformation thereby having high ductility.
Therefore, there is a need for a torsionally strong, fully hardened, high ductility guidewire.